FileCache's
cacheout
function lets you work with more output files than your operating system lets you have open at any one time. If you use it to open an existing file that FileCache is seeing for the first time, the file is truncated to length zero, no questions asked. However, in its opening and closing of files in the background,
cacheout
tracks the files it has opened before and does not overwrite them, but appends to them instead. This does not create directories for you, so if you give it
/usr/local/dates/merino.ewe
to open but the directory
/usr/local/dates
doesn't exist,
cacheout
will
die
.

The
cacheout()
function checks the value of the C-level constant
NOFILE from the standard system include file
sys/param.h
to determine how many concurrently open files are allowed on your system. This value can be incorrect on some systems and even missing on a few (for instance, on those where the maximum number of open file descriptors is a process resource limit that can be set with the
limit
or
ulimit
commands). If
cacheout()
can't get a value for NOFILE, just set
$FileCache::maxopen
to be four less than the correct value, or choose a reasonable number by trial and error.

Example 7.8
splits an
xferlog
file created by the popular
wuftpd
FTP server into files named after the authenticated user. The fields in
xferlog
files are space-separated, and the fourth from last field is the authenticated username.